The occurrence of severe mitral regurgitation (MR) immediately following mitral valve replacement (MRV) is exceedingly rare. One cause is interference with closure of a prosthetic occluder by the left ventricular wall, calcific deposits or residual unexcised mitral leaflet or chordae tendineae. Another cause is incomplete obliteration by suture of the space between the prosthetic or bioprosthetic ring and the native anulus resulting in a paraanular communication. A third and hitherto unreported cause of severe MR immediately following MVR by a bioprosthesis was described. It was due to sutures, which encircled 2 of the 3 bioprosthetic stents, and tautened the cusps producing severe MR. The left atrium should not be closed after MVR until it is clear that the cusps of a tissue valve, or the occluder of a mechanical valve, are freely mobile.